| 简介 |
PROBLEM TO BE SOLVED : To provide a high strength and high ductility cold rolled steel sheet which has no generation of surface defects in a slab, and has excellent ductility, spot weldability and press formability as well. SOLUTION : The steel sheet has a composition containing 0.05 to 0.40% C, 0.5 to 3.0% Si, 0.5 to 3.0% Mn, =30% ferrite and retained &gamma of >=3% by the average in the total sheet thickness direction, and in which the content of residual &gamma in the region from the steel sheet surface to a position of 1/16 in the sheet thickness is =2.5 is preferably satisfied. The steel sheet may contain one or two kinds of Nb and V, and one or more kinds selected from Cr, Mo and B. |
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